Polymers, resist compositions and patterning process

ABSTRACT

A resist composition comprising a copolymer of an acrylic ester monomer containing fluorine at α-position with a norbornene derivative containing oxygen or sulfur within the norbornene ring as a base resin is sensitive to high-nergy radiation below 200 nm, has excellent sensitivity, transparency and dry etching resistance, and is suited for lithographic microprocessing.

[0001] This invention relates to polymers useful as the base resin inresist compositions suited for microfabrication. It also relates toresist compositions, especially chemical amplification resistcompositions comprising the polymers, and a patterning process using thesame.

BACKGROUND OF THE INVENTION

[0002] In the drive for higher integration and operating speeds in LSIdevices, the pattern rule is made drastically finer. The rapid advancetoward finer pattern rules is grounded on the development of aprojection lens with an increased NA, a resist material with improvedperformance, and exposure light of a shorter wavelength. To the demandfor a resist material with a higher resolution and sensitivity, chemicalamplification positive working resist materials which are catalyzed byacids generated upon light exposure are effective as disclosed in U.S.Pat. No. 4,491,628 and U.S. Pat. No. 5,310,619 (JP-B 2-27660 and JP-A63-27829). They now become predominant resist materials especiallyadapted for deep UV lithography. Also, the change-over from i-line (365nm) to shorter wavelength KrF laser (248 nm) brought about a significantinnovation. Resist materials adapted for KrF excimer lasers enjoyedearly use on the 0.3 micron process, passed through the 0.25 micronrule, and currently entered the mass production phase on the 0.18 micronrule. Engineers have started investigation on the 0.15 micron rule, withthe trend toward a finer pattern rule being accelerated.

[0003] For ArF laser (193 nm), it is expected to enable miniaturizationof the design rule to 0.13 μm or less. Since conventionally used novolacresins and polyvinylphenol resins have very strong absorption inproximity to 193 nm, they cannot be used as the base resin for resists.To ensure transparency and dry etching resistance, some engineersinvestigated acrylic and alicyclic (typically cycloolefin) resins asdisclosed in JP-A 9-73173, JP-A 10-10739, JP-A 9-230595 and WO 97/33198.

[0004] With respect to F₂ excimer laser (157 nm) which is expected toenable further miniaturization to 0.10 μm or less, more difficultyarises in insuring transparency because it was found that acrylic resinswhich are used as the base resin for ArF are not transmissive to lightat all and those cycloolefin resins having carbonyl bonds have strongabsorption. It was also found that poly(vinyl phenol) which is used asthe base resin for KrF has a window for absorption in proximity to 160nm, so the transmittance is somewhat improved, but far below thepractical level.

SUMMARY OF THE INVENTION

[0005] An object of the invention is to provide a novel polymer having ahigh transmittance to vacuum ultraviolet radiation of up to 300 nm,especially F₂ (157 nm), Kr₂ (146 nm), KrAr (134 nm) and Ar₂ (126 nm)excimer laser beams, and useful as the base resin in a resistcomposition. Another object is to provide a resist composition, andespecially a chemical amplification resist composition, comprising thepolymer, and a patterning process using the same.

[0006] It has been found that when a copolymer of an acrylic estermonomer containing fluorine at a-position with a norbornene derivativecontaining oxygen or sulfur within the norbornene ring is used as a baseresin, the resulting chemically amplified resist composition isdrastically improved in transparency and adhesion and fully resistant todry etching.

[0007] In a first aspect, the invention provides a polymer comprisingrecurring units of the following general formulae (1a) and (1b) andhaving a weight average molecular weight of 1,000 to 500,000.

[0008] Herein R¹ and R² each are hydrogen, a fluorine atom or astraight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20carbon atoms; R³ is a fluorine atom or a straight, branched or cyclicfluorinated alkyl group of 1 to 20 carbon atoms; R⁴ is an acid labilegroup, an adhesive group or a straight, branched or cyclic fluorinatedalkyl group of 1 to 20 carbon atoms; R⁵ is an oxygen or sulfur atom;R^(6a), R^(6b), R^(6c) and R^(6d) are each independently hydrogen, ahydroxyl group, —(CH₂)_(d)C(R⁷)₂(OR⁸), —(CH₂)_(d)CO₂R⁸, or a straight,branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbonatoms which can contain oxygen in the form of a hydroxyl group or etherbond in a substituent group, wherein R⁷ is hydrogen, a fluorine atom ora straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbonatoms, R⁸ is hydrogen, an acid labile group, an adhesive group, or astraight, branched or cyclic fluorinated alkyl group of 1 to 20 carbonatoms, and 0<d≦6; letters a, b and c are 0<a<1, 0<b<1, 0<a+b≦1, and c=0or 1. Most often, R³ is trifluoromethyl.

[0009] In a second aspect, the invention provides a resist compositioncomprising the polymer, and preferably a chemically amplified positiveresist composition comprising (A) the polymer, (B) an organic solvent,(C) a photoacid generator, and optionally (D) a basic compound and/or(E) a dissolution inhibitor.

[0010] In a third aspect, the invention provides a process for forming aresist pattern comprising the steps of applying the resist compositiondefined above onto a substrate to form a coating; heat treating thecoating and then exposing it to high-energy radiation in a wavelengthband of 100 to 180 nm or 1 to 30 nm through a photo mask; and optionallyheat treating the exposed coating and developing it with a developer.The high-energy radiation is typically an F₂ laser beam, Ar₂ laser beamor soft x-ray.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Polymer

[0012] For improving the transmittance in proximity to 157 nm, reducingthe number of carbonyl groups and/or carbon-to-carbon double bonds iscontemplated to be one effective way. It was also found that introducingfluorine atoms into base polymers makes a great contribution to improvedtransmittance. In fact, poly(vinyl phenol) having fluorine introduced inits aromatic rings offers a transmittance nearly on a practicallyacceptable level. However, this base polymer was found to turn to benegative upon exposure to high-energy radiation as from an F₂ excimerlaser, interfering with its use as a practical resist. In contrast,those polymers obtained by introducing fluorine into acrylic resins orpolymers containing in their backbone an alicyclic compound originatingfrom a norbornene derivative were found to be suppressed in absorptionand overcome the negative turning problem.

[0013] It has been found that copolymers comprising recurring units ofthe formulae (1a) and (1b), shown below, maintain high transparency at awavelength of nearly 157 nm and have improved dry etching resistance.

[0014] In formulae (1a) and (1b), R¹ and R² each are hydrogen, afluorine atom or a straight, branched or cyclic alkyl or fluorinatedalkyl group of 1 to 20 carbon atoms; R³ is a fluorine atom or astraight, branched or cyclic fluorinated alkyl group of 1 to 20 carbonatoms; R⁴ is an acid labile group, an adhesive group or a straight,branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms; R⁵is an oxygen or sulfur atom; R^(6a), R^(6b), R^(6c) and R^(6d) are eachindependently hydrogen, a hydroxyl group, —(CH₂)_(d)C(R⁷)₂(OR⁸),—(CH₂)_(d)CO₂R⁸, or a straight, branched or cyclic alkyl or fluorinatedalkyl group of 1 to 20 carbon atoms which may contain oxygen in the formof a hydroxyl group or ether bond in a substituent group; R⁷ ishydrogen, a fluorine atom or a straight, branched or cyclic fluorinatedalkyl group of 1 to 20 carbon atoms; R⁸ is hydrogen, an acid labilegroup, an adhesive group, or a straight, branched or cyclic fluorinatedalkyl group of 1 to 20 carbon atoms; letters a and b each are a numberfrom more than 0 to less than 1, and 0<a+b≦1, c is 0 or 1, and d is anumber of 0 to 6.

[0015] Suitable straight, branched or cyclic alkyl groups are of 1 to 20carbon atoms, preferably 1 to 12 carbon atoms, especially 1 to 10 carbonatoms and include, but are not limited to, methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl,2-ethylhexyl, and n-octyl. Suitable fluorinated alkyl groups correspondto the foregoing alkyl groups in which some or all of the hydrogen atomsare substituted with fluorine atoms, and include, for example,trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl,1,1,1,3,3,3-hexafluoroisopropyl, and 1,1,2,2,3,3,3-heptafluoropropyl.

[0016] The acid labile groups represented by R⁴ and R⁸ are selected froma variety of such groups, preferably from among the groups of thefollowing formulae (2) to (4).

[0017] In formula (2), R⁹ is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms or a group of formula (4). Suitable tertiary alkyl groupsinclude tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Suitable oxoalkyl groups include 3-oxocyclohexyl,4-methyl-2-oxooxan-4-yl, and 5-methyl-5-oxooxolan-4-yl. Letter e is aninteger of 0 to 6.

[0018] Illustrative, non-limiting, examples of the acid labile group offormula (2) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl,tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl,1,1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxycarbonylmethyl,1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopentyloxycarbonylmethyl,1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl groups.

[0019] In formula (3), R¹⁰ and R¹¹ are hydrogen or straight, branched orcyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbonatoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl andn-octyl. R¹² is a monovalent hydrocarbon group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms, which may contain a hetero atom such asoxygen, for example, straight, branched or cyclic alkyl groups andsubstituted ones of these alkyl groups in which some hydrogen atoms aresubstituted with hydroxyl, alkoxy, oxo, amino or alkylamino groups.Exemplary substituted alkyl groups are shown below.

[0020] —(CH₂)₄—OH —(CH₂)₆—OH

[0021] —(CH₂)₂—O—(CH₂)₃CH₃ —(CH₂)₂—O—(CH₂)₂—OH

[0022] A pair of R¹⁰ and R¹¹, a pair of R¹⁰ and R¹², or a pair of R¹¹and R¹² may bond together to form a ring. Each of R¹⁰, R¹¹ and R¹² is astraight or branched alkylene group of 1 to 18 carbon atoms, preferably1 to 10 carbon atoms, when they form a ring.

[0023] Of the acid labile groups of formula (3), straight or branchedones are exemplified by the following groups.

[0024] —CH₂—O—CH₃ —CH₂—O—CH₂CH₃ —CH₂—O—(CH₂)₂CH₃ —CH₂—O—(CH₂)₃CH₃

[0025] Of the acid labile groups of formula (3), cyclic ones areexemplified by tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

[0026] Of the groups of formula (3), ethoxyethyl, butoxyethyl andethoxypropyl are preferred.

[0027] In formula (4), R¹³, R¹⁴ and R¹⁵ each are a monovalenthydrocarbon group, typically a straight, branched or cyclic alkyl groupof 1 to 20 carbon atoms, which may contain a hetero atom such as oxygen,sulfur, nitrogen or fluorine. A pair of R¹³ and R¹⁴, R¹³ and R¹⁵, andR¹⁴ and R¹⁵, taken together, may form a ring with the carbon atom towhich they are bonded.

[0028] Examples of the tertiary alkyl group represented by formula (4)include tert-butyl, triethylcarbyl, 1-ethylnorbornyl,1-methylcyclohexyl, 1-ethylcyclopentyl, 2-(2-methyl)adamantyl,2-(2-ethyl)adamantyl, tert-amyl,1,1,1,3,3,3-hexafluoro-2-methyl-isopropyl, and1,1,1,3,3,3-hexafluoro-2-cyclohexyl-isopropyl as well as the groupsshown below.

[0029] Herein, R¹⁶ is a straight, branched or cyclic alkyl group of 1 to6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, n-pentyl, n-hexyl, cyclopropyl, cyclopropylmethyl,cyclobutyl, cyclopentyl and cyclohexyl. R¹⁷ is a straight, branched orcyclic alkyl group of 2 to 6 carbon atoms, such as ethyl, propyl,isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, cyclopropyl,cyclopropylmethyl, cyclobutyl, cyclopentyl and cyclohexyl. Each of R¹⁸and R¹⁹ is hydrogen, a monovalent hydrocarbon group of 1 to 6 carbonatoms which may contain a hetero atom, or a monovalent hydrocarbon groupof 1 to 6 carbon atoms which may be separated by a hetero atom. Thesegroups may be straight, branched or cyclic. The hetero atom is typicallyselected from oxygen, sulfur and nitrogen atoms and may be contained orintervene in the form of —OH, —OR²⁰, —O—, —S—, —S(═O)—, —NH₂, —NHR²⁰,—N(R²⁰)₂, —NH— or —NR²⁰— wherein R²⁰ is an alkyl group. Examples of R¹⁸and R¹⁹ groups include methyl, hydroxymethyl, ethyl, hydroxyethyl,propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, methoxy,methoxymethoxy, ethoxy and tert-butoxy.

[0030] Next, the adhesive groups represented by R⁴ and R⁸ are selectedfrom a variety of such groups, preferably from among the groups of thefollowing formulae.

[0031] To improve the transparency of the inventive resin, R⁴ and R⁸ maystand for straight, branched or cyclic fluorinated alkyl groups of 1 to20 carbon atoms. Illustrative examples include trifluoromethyl,2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl,1,1,1,3,3,3-hexafluoroisopropyl, 1,1,2,2,3,3,3-heptafluoropropyl, and2,2,3,3,4,4,5,5-octafluoropentyl, as well as the groups shown below.

[0032] Herein, R²¹ is hydrogen, a fluorine atom, or a straight, branchedor cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, ande is an integer of 0 to 10.

[0033] In the polymers of the invention, one or more units selected fromthe recurring units (5-1) to (5-5), shown below, may be incorporated inaddition to the above recurring units in order to improve the acidelimination, adhesion and transparency of the resin.

[0034] Herein, each of R²² to R²⁴ is hydrogen, fluorine or a straight,branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbonatoms; R²⁵ is an acid labile group, an adhesive group, as mentionedabove, or a straight, branched or cyclic fluorinated alkyl group of 1 to20 carbon atoms; R²⁶ is a methylene group, oxygen atom or sulfur atom;each of R²⁷ and R²⁸ is hydrogen, methyl or CH₂CO₂R³⁰ wherein R³⁰ is astraight, branched or cyclic alkyl or substituted alkyl group of 1 to 20carbon atoms; R²⁹ is a straight, branched or cyclic alkylene orfluorinated alkylene group of 1 to 20 carbon atoms; and c is 0 or 1.

[0035] Besides the units (5-1) to (5-5), adhesive units as shown belowmay also be incorporated in the inventive polymers for the purpose offurther improving adhesion.

[0036] Herein, each of R³² to R³³ is hydrogen, fluorine or a straight,branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbonatoms; f and g each are an integer of 0 to 4, and 0≦f+g≦4.

[0037] Furthermore, norbornene units containing an adhesive group asshown below may also be incorporated in the inventive polymers.

[0038] It is also possible to improve the adhesion of the inventivepolymers by incorporating therein styrene derivatives havinghexafluoroisopropyl alcohol as shown below.

[0039] Besides the units (5-1) to (5-5), transparent units as shownbelow may also be incorporated in the inventive polymers for the purposeof improving transparency.

[0040] Herein, each of R³⁴ to R³⁷ is fluorine, hydrogen or a fluorinatedalkyl group of 1 to 4 carbon atoms, at least one of R³⁴ to R³⁷ containsfluorine; each of R³⁸ and R³⁹ is hydrogen, methyl or trifluoromethyl.

[0041] The polymer of the invention is generally synthesized bydissolving monomers corresponding to the respective units of formulae(1a) and (1b) and optionally, an adhesion-improving monomer and the likein a solvent, adding a catalyst thereto, and effecting polymerizationreaction while heating or cooling the system if necessary. Thepolymerization reaction depends on the type of initiator or catalyst,trigger means (including light, heat, radiation and plasma), andpolymerization conditions (including temperature, pressure,concentration, solvent, and additives). Commonly used for preparation ofthe polymer of the invention are radical polymerization of triggeringpolymerization with radicals of 2,2′-azobisisobutyronitrile (AIBN) orthe like, and ion (anion) polymerization using catalysts such as alkyllithium. These polymerization steps may be carried out in theirconventional manner.

[0042] The radical polymerization initiator used herein is not critical.Exemplary initiators include azo compounds such as AIBN,2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), and2,2′-azobis(2,4,4-trimethylpentane); peroxide compounds such astert-butyl peroxypivalate, lauroyl peroxide, benzoyl peroxide andtert-butyl peroxylaurate; water-soluble initiators, for example,persulfate salts such as potassium persulfate; and redox combinations ofpotassium persulfate or peroxides such as hydrogen peroxide withreducing agents such as sodium sulfite. The amount of the polymerizationinitiator used is determined as appropriate in accordance with suchfactors as the identity of initiator and polymerization conditions,although the amount is often in the range of about 0.001 to 5% byweight, especially about 0.01 to 2% by weight based on the total weightof monomers to be polymerized.

[0043] For the polymerization reaction, a solvent may be used. Thepolymerization solvent used herein is preferably one which does notinterfere with the polymerization reaction. Typical solvents includeester solvents such as ethyl acetate and n-butyl acetate, ketonesolvents such as acetone, methyl ethyl ketone and methyl isobutylketone, aliphatic or aromatic hydrocarbon solvents such as toluene,xylene and cyclohexane, alcohol solvents such as isopropyl alcohol andethylene glycol monomethyl ether, and ether solvents such as diethylether, dioxane, and tetrahydrofuran. These solvents may be used alone orin admixture of two or more. Further, any of well-known molecular weightmodifiers such as dodecylmercaptan may be used in the polymerizationsystem.

[0044] The temperature of polymerization reaction varies in accordancewith the identity of polymerization initiator and the boiling point ofthe solvent although it is often preferably in the range of about 20 to200° C., and especially about 50 to 140° C. Any desired reactor orvessel may be used for the polymerization reaction.

[0045] From the solution or dispersion of the polymer thus obtained, theorganic solvent or water serving as the reaction medium is removed byany of well-known techniques. Suitable techniques include, for example,re-precipitation followed by filtration, and heat distillation undervacuum.

[0046] Desirably the polymer has a weight average molecular weight ofabout 1,000 to about 1,000,000, and especially about 2,000 to about100,000.

[0047] The inventive polymer can be represented by the formula:

-(U1)_(h1)-(U2)_(h2)-(U3)h₃-

[0048] wherein U1 represents units of formula (1a), U2 represents unitsof formula (1b), U3 represents units of formulae (5-1) to (5-5),adhesive units and transparent units, and h1+h2+h3=1. It is preferredthat h1, h2 and h3 fall in the range:

[0049] 0.1≦h1/(h1+h2+h3)≦0.9, especially 0.2≦h1/(h1+h2+h3)≦0.8,

[0050] 0.1≦h2/(h1+h2+h3)≦0.8, especially 0.2≦h2/(h1+h2+h3)≦0.5, and

[0051] 0≦h3/(h1+h2+h3)≦0.5, especially 0≦h3/(h1+h2+h3)≦0.3.

[0052] The polymer of the invention can be used as a base resin inresist compositions, specifically chemical amplification type resistcompositions, and especially chemical amplification type positiveworking resist compositions. It is understood that the polymer of theinvention may be admixed with another polymer for the purpose ofaltering the dynamic properties, thermal properties, alkali solubilityand other physical properties of polymer film. The type of the otherpolymer which can be admixed is not critical. Any of polymers known tobe useful in resist use may be admixed in any desired proportion.

[0053] Resist Composition

[0054] As long as the polymer of the invention is used as a base resin,the resist composition of the invention may be prepared using well-knowncomponents. In a preferred embodiment, the chemically amplified positiveresist composition is defined as comprising (A) the above-definedpolymer as a base resin, (B) an organic solvent, and (C) a photoacidgenerator. In the resist composition, there may be further formulated(D) a basic compound and/or (E) a dissolution inhibitor.

[0055] Component (B)

[0056] The organic solvent used as component (B) in the invention may beany organic solvent in which the base resin (inventive polymer),photoacid generator, and other components are soluble. Illustrative,non-limiting, examples of the organic solvent include ketones such ascyclohexanone and methyl-2-n-amylketone; alcohols such as3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; and esters such as propylene glycolmonomethyl ether acetate, propylene glycol monoethyl ether acetate,ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,tert-butyl propionate, and propylene glycol mono-tert-butyl etheracetate.

[0057] Also useful are fluorinated organic solvents. Illustrative,non-limiting examples include 2-fluoroanisole, 3-fluoroanisole,4-fluoroanisole, 2,3-difluoroanisole, 2,4-difluoroanisole,2,5-difluoroanisole, 5,8-difluoro-1,4-benzodioxane, 2,3-difluorobenzylalcohol, 1,3-difluoro-2-propanol, 2′,4′-difluoropropiophenone,2,4-difluorotoluene, trifluoroacetaldehyde ethyl hemiacetal,trifluoroacetamide, trifluoroethanol, 2,2,2-trifluoroethyl butyrate,ethyl heptafluorobutyrate, ethyl heptafluorobutylacetate, ethylhexafluoroglutarylmethyl, ethyl 3-hydroxy-4,4,4-trifluorobutyrate, ethyl2-methyl-4,4,4-trifluoroacetoacetate, ethyl pentafluorobenzoate, ethylpentafluoropropionate, ethyl pentafluoropropynylacetate, ethylperfluorooctanoate, ethyl 4,4,4-trifluoroacetoacetate, ethyl4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorocrotonate, ethyltrifluorosulfonate, ethyl 3-(trifluoromethyl)butyrate, ethyltrifluoropyruvate, sec-ethyl trifluoroacetate, fluorocyclohexane,2,2,3,3,4,4,4-heptafluoro-1-butanol,1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione,1,1,1,3,5,5,5-heptafluoropentane-2,4-dione,3,3,4,4,5,5,5-heptafluoro-2-pentanol,3,3,4,4,5,5,5-heptafluoro-2-pentanone, isopropyl4,4,4-trifluoroacetoacetate, methyl perfluorodecanoate, methylperfluoro(2-methyl-3-oxahexanoate), methyl perfluorononanoate, methylperfluorooctanoate, methyl 2,3,3,3-tetrafluoropropionate, methyltrifluoroacetoacetate, 1,1,1,2,2,6,6,6-octafluoro-2,4-hexanedione,2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 1H,1H,2H,2H-perfluoro-1-decanol,perfluoro-2,5-dimethyl-3,6-dioxane anionic acid methyl ester,2H-perfluoro-5-methyl-3,6-dioxanonane,1H,1H,2H,3H,3H-perfluorononane-1,2-diol, 1H,1H,9H-perfluoro-1-nonanol,1H,1H-perfluorooctanol, 1H,1H,2H,2H-perfluorooctanol,2H-perfluoro-5,8,11,14-tetramethyl-3,6,9,12,15-pentaoxaoctadecane,perfluorotributylamine, perfluorotrihexylamine, methylperfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoate,perfluorotripentylamine, perfluorotripropylamine,1H,1H,2H,3H,3H-perfluoroundecane-1,2-diol,trifluorobutanol-1,1,1-trifluoro-5-methyl-2,4-hexanedione,1,1,1-trifluoro-2-propanol, 3,3,3-trifluoro-1-propanol,1,1,1-trifluoro-2-propyl acetate, perfluorobutyltetrahydrofuran,perfluorodecalin, perfluoro(1,2-dimethylcyclohexane),perfluoro(1,3-dimethylcyclohexane), propylene glycol trifluoromethylether acetate, propylene glycol methyl ether trifluoromethyl acetate,butyl trifluoromethylacetate, methyl 3-trifluoromethoxypropionate,perfluorocyclohexanone, propylene glycol trifluoromethyl ether, butyltrifluoroacetate, and 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione.

[0058] These solvents may be used alone or in combinations of two ormore thereof. Of the above organic solvents, preferred are diethyleneglycol dimethyl ether and 1-ethoxy-2-propanol, in which the photoacidgenerator is most soluble, and propylene glycol monomethyl ether acetatewhich is safe, and mixtures thereof.

[0059] The solvent is preferably used in an amount of about 300 to10,000 parts by weight, more preferably about 500 to 5,000 parts byweight per 100 parts by weight of the base resin.

[0060] Component (C)

[0061] Suitable examples of the photoacid generator (C) include oniumsalts of formula (5) below, diazomethane derivatives of formula (6),glyoxime derivatives of formula (7), β-ketosulfone derivatives,disulfone derivatives, nitrobenzylsulfonate derivatives, sulfonic acidester derivatives, and imidoyl sulfonate derivatives.

[0062] The onium salts used as the photoacid generator are of thegeneral formula (5).

(R⁴⁰)_(i)M⁺K⁻  (5)

[0063] In the formula, R⁴⁰ is a straight, branched or cyclic alkyl of 1to 12 carbon atoms, an aryl of 6 to 20 carbon atoms, or an aralkyl of 7to 12 carbon atoms; M⁺ is iodonium or sulfonium; K⁻ is anon-nucleophilic counter-ion; and the letter i is 2 or 3.

[0064] Illustrative examples of alkyl groups represented by R⁴⁰ includemethyl, ethyl, propyl, butyl, pentyl, 2-oxocyclopentyl, norbornyl, andadamantyl. Exemplary aryl groups include phenyl; alkoxyphenyl groupssuch as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl,p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groupssuch as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl,4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary aralkylgroups include benzyl and phenethyl. Examples of the non-nucleophiliccounter-ion represented by K⁻ include halide ions such as chloride andbromide; fluoroalkylsulfonate ions such as triflate,1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate;arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; andalkylsulfonate ions such as mesylate and butanesulfonate.

[0065] The diazomethane derivatives used as the photoacid generator areof the general formula (6).

[0066] In the formula, R⁴¹ and R⁴² are straight, branched or cyclicalkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl orhalogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7to 12 carbon atoms.

[0067] Illustrative examples of alkyl groups represented by R⁴¹ and R⁴²include methyl, ethyl, propyl, butyl, amyl, cyclopentyl, cyclohexyl,norbornyl, and adamantyl. Exemplary halogenated alkyl groups includetrifluoromethyl, 2,2,2-trifluoroethyl, 2,2,2-trichloroethyl, andnonafluorobutyl. Exemplary aryl groups include phenyl; alkoxyphenylgroups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl,ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; andalkylphenyl groups such as 2-methylphenyl, 3-methylphenyl,4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, anddimethylphenyl. Exemplary halogenated aryl groups include fluorophenyl,chlorophenyl, and 1,2,3,4,5-pentafluorophenyl. Exemplary aralkyl groupsinclude benzyl and phenethyl.

[0068] The glyoxime derivatives used as the photoacid generator are ofthe general formula (7).

[0069] In the formula, R⁴³ to R⁴⁵ are straight, branched or cyclic alkylor halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenatedaryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7 to 12 carbonatoms. R⁴⁴ and R⁴⁵ may together form a cyclic structure with the provisothat if they form a cyclic structure, each is a straight or branchedalkylene group of 1 to 6 carbon atoms.

[0070] The alkyl, halogenated alkyl, aryl, halogenated aryl, and aralkylgroups represented by R⁴³ to R⁴⁵ are exemplified by the same groups asmentioned above for R⁴¹ and R⁴². Examples of alkylene groups representedby R⁴⁴ and R⁴⁵ include methylene, ethylene, propylene, butylene, andhexylene.

[0071] Illustrative, non-limiting examples of the photoacid generatorsinclude:

[0072] onium salts such as diphenyliodonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate,diphenyliodonium p-toluenesulfonate, (p-tert-butoxyphenyl)phenyliodoniump-toluenesulfonate, triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate,tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate,triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfoniumbutanesulfonate, trimethylsulfonium trifluoromethanesulfonate,trimethylsulfonium p-toluenesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate,dimethylphenylsulfonium trifluoromethanesulfonate,dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfoniumtrifluoromethanesulfonate, dicyclohexylphenylsulfoniump-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,ethylenebis[methyl(2-oxocyclopentyl)sulfoniumtrifluoromethanesulfonate], and1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate; diazomethanederivatives such as bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane, bis(xylenesulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane,bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane,bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane,bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane,bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane,bis(isoamylsulfonyl)diazomethane, bis(sec-amylsulfonyl)diazomethane,bis(tert-amylsulfonyl)diazomethane,1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)diazomethane,1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)diazomethane, and1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane; glyoximederivatives such as bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime,bis-O-(p-toluenesulfonyl)-α-diphenylglyoxime,bis-O-(p-toluenesulfonyl)-α-dicyclohexylglyoxime,bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime,bis-O-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-O-(n-butanesulfonyl)-α-dimethylglyoxime,bis-O-(n-butanesulfonyl)-α-diphenylglyoxime,bis-O-(n-butanesulfonyl)-α-dicyclohexylglyoxime,bis-O-(n-butanesulfonyl)-2,3-pentanedioneglyoxime,bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-O-(methanesulfonyl)-α-dimethylglyoxime,bis-O-(trifluoromethanesulfonyl)-α-dimethylglyoxime,bis-O-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime,bis-O-(tert-butanesulfonyl)-α-dimethylglyoxime,bis-O-(perfluorooctanesulfonyl)-α-dimethylglyoxime,bis-O-(cyclohexanesulfonyl)-α-dimethylglyoxime,bis-O-(benzenesulfonyl)-α-dimethylglyoxime,bis-O-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime,bis-O-(p-tert-butylbenzenesulfonyl)-α-dimethylglyoxime,bis-O-(xylenesulfonyl)-α-dimethylglyoxime, andbis-O-(camphorsulfonyl)-α-dimethylglyoxime; ketosulfone derivatives suchas 2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane and2-isopropylcarbonyl-2-(p-toluenesulfonyl)propane; disulfone derivativessuch as diphenyl disulfone and dicyclohexyl disulfone; nitrobenzylsulfonate derivatives such as 2,6-dinitrobenzyl p-toluenesulfonate and2,4-dinitrobenzyl p-toluenesulfonate; sulfonic acid ester derivativessuch as 1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; and imidoyl sulfonatederivatives such as phthalimidoyl triflate, phthalimidoyl tosylate,5-norbornene-2,3-dicarboxyimidoyl triflate,5-norbornene-2,3-dicarboxyimidoyl tosylate, and5-norbornene-2,3-dicarboxyimidoyl n-butylsulfonate.

[0073] Preferred among these photoacid generators are onium salts suchas triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate,trinaphthylsulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocylohexyl)sulfonium trifluoromethanesulfonate,and 1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate;diazomethane derivatives such as bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane,bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane,bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane,bis(isopropylsulfonyl)diazomethane, andbis(tert-butylsulfonyl)diazomethane; and glyoxime derivatives such asbis-O-(p-toluenesulfonyl)-α-dimethylglyoxime andbis-O-(n-butanesulfonyl)-α-dimethylglyoxime. These photoacid generatorsmay be used singly or in combinations of two or more thereof. Oniumsalts are effective for improving rectangularity, while diazomethanederivatives and glyoxime derivatives are effective for reducing standingwaves. The combination of an onium salt with a diazomethane or aglyoxime derivative allows for fine adjustment of the profile.

[0074] The photoacid generator is preferably added in an amount of about0.2 to 15 parts by weight per 100 parts by weight of the base resin. Atless than 0.2 part, the amount of acid generated during exposure wouldbe too small and the sensitivity and resolution be poor, whereas theaddition of more than 15 parts would lower the transparency of theresist and result in a poor resolution.

[0075] Component (D)

[0076] The basic compound used as component (D) is preferably a compoundcapable of suppressing the rate of diffusion when the acid generated bythe photoacid generator diffuses within the resist film. The inclusionof this type of basic compound holds down the rate of acid diffusionwithin the resist film, resulting in better resolution. In addition, itsuppresses changes in sensitivity following exposure, thus reducingsubstrate and environment dependence, as well as improving the exposurelatitude and the pattern profile. See JP-A 5-232706, 5-249683, 5-158239,5-249662, 5-257282, 5-289322, and 5-289340.

[0077] Examples of suitable basic compounds include ammonia, primary,secondary, and tertiary aliphatic amines, mixed amines, aromatic amines,heterocyclic amines, carboxyl group-bearing nitrogenous compounds,sulfonyl group-bearing nitrogenous compounds, hydroxyl group-bearingnitrogenous compounds, hydroxyphenyl group-bearing nitrogenouscompounds, alcoholic nitrogenous compounds, amide derivatives, and imidederivatives.

[0078] Examples of suitable primary aliphatic amines includemethylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, pentylamine,tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine,heptylamine, octylamine, nonylamine, decylamine, dodecylamine,cetylamine, methylenediamine, ethylenediamine, andtetraethylenepentamine. Examples of suitable secondary aliphatic aminesinclude dimethylamine, diethylamine, di-n-propylamine,di-iso-propylamine, di-n-butylamine, di-iso-butylamine,di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine,dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, didodecylamine, dicetylamine,N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, andN,N-dimethyltetraethylenepentamine. Examples of suitable tertiaryaliphatic amines include trimethylamine, triethylamine,tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine,tri-iso-butylamine, tri-sec-butylamine, tripentylamine,tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, tridodecylamine,tricetylamine, N,N,N′,N′-tetramethylmethylenediamine,N,N,N′,N′-tetramethylethylenediamine, andN,N,N′,N′-tetramethyltetraethylenepentamine.

[0079] Examples of suitable mixed amines include dimethylethylamine,methylethylpropylamine, benzylamine, phenethylamine, andbenzyldimethylamine. Examples of suitable aromatic amines includeaniline derivatives (e.g., aniline, N-methylaniline, N-ethylaniline,N-propylaniline, N,N-dimethylaniline, 2-methylaniline, 3-methylaniline,4-methylaniline, ethylaniline, propylaniline, trimethylaniline,2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline,2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyltoluidine),diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine,phenylenediamine, naphthylamine, and diaminonaphthalene. Examples ofsuitable heterocyclic amines include pyrrole derivatives (e.g., pyrrole,2H-pyrrole, 1-methylpyrrole, 2,4-dimethylpyrrole, 2,5-dimethylpyrrole,and N-methylpyrrole), oxazole derivatives (e.g., oxazole andisooxazole), thiazole derivatives (e.g., thiazole and isothiazole),imidazole derivatives (e.g., imidazole, 4-methylimidazole, and4-methyl-2-phenylimidazole), pyrazole derivatives, furazan derivatives,pyrroline derivatives (e.g., pyrroline and 2-methyl-1-pyrroline),pyrrolidine derivatives (e.g., pyrrolidine, N-methylpyrrolidine,pyrrolidinone, and N-methylpyrrolidone), imidazoline derivatives,imidazolidine derivatives, pyridine derivatives (e.g., pyridine,methylpyridine, ethylpyridine, propylpyridine, butylpyridine,4-(1-butylpentyl)pyridine, dimethylpyridine, trimethylpyridine,triethylpyridine, phenylpyridine, 3-methyl-2-phenylpyridine,4-tert-butylpyridine, diphenylpyridine, benzylpyridine, methoxypyridine,butoxypyridine, dimethoxypyridine, 1-methyl-2-pyridine,4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine,2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine),pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives,pyrazoline derivatives, pyrazolidine derivatives, piperidinederivatives, piperazine derivatives, morpholine derivatives, indolederivatives, isoindole derivatives, 1H-indazole derivatives, indolinederivatives, quinoline derivatives (e.g., quinoline and3-quinolinecarbonitrile), isoquinoline derivatives, cinnolinederivatives, quinazoline derivatives, quinoxaline derivatives,phthalazine derivatives, purine derivatives, pteridine derivatives,carbazole derivatives, phenanthridine derivatives, acridine derivatives,phenazine derivatives, 1,10-phenanthroline derivatives, adeninederivatives, adenosine derivatives, guanine derivatives, guanosinederivatives, uracil derivatives, and uridine derivatives.

[0080] Examples of suitable carboxyl group-bearing nitrogenous compoundsinclude aminobenzoic acid, indolecarboxylic acid, nicotinic acid, andamino acid derivatives (e.g. alanine, alginine, aspartic acid, glutamicacid, glycine, histidine, isoleucine, glycylleucine, leucine,methionine, phenylalanine, threonine, lysine,3-aminopyrazine-2-carboxylic acid, and methoxyalanine).

[0081] Examples of suitable sulfonyl group-bearing nitrogenous compoundsinclude 3-pyridinesulfonic acid and pyridinium p-toluenesulfonate.

[0082] Examples of suitable hydroxyl group-bearing nitrogenouscompounds, hydroxyphenyl group-bearing nitrogenous compounds, andalcoholic nitrogenous compounds include 2-hydroxypyridine, aminocresol,2,4-quinolinediol, 3-indolemethanol hydrate, monoethanolamine,diethanolamine, triethanolamine, N-ethyldiethanolamine,N,N-diethylethanolamine, triisopropanolamine, 2,2′-iminodiethanol,2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol,4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine,1-(2-hydroxyethyl)piperazine, 1-[2-(2-hydroxyethoxy)ethyl]piperazine,piperidine ethanol, 1-(2-hydroxyethyl)pyrrolidine,1-(2-hydroxyethyl)-2-pyrrolidinone, 3-piperidino-1,2-propanediol,3-pyrrolidino-1,2-propanediol, 8-hydroxyjulolidine, 3-quinuclidinol,3-tropanol, 1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol,N-(2-hydroxyethyl)phthalimide, and N-(2-hydroxyethyl)isonicotinamide.

[0083] Examples of suitable amide derivatives include formamide,N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide,N,N-dimethylacetamide, propionamide, and benzamide. Suitable imidederivatives include phthalimide, succinimide, and maleimide.

[0084] In addition, basic compounds of the following general formula (8)may also be included alone or in admixture.

 —R⁴⁸—O—R⁴⁹  (8a)

[0085] In the formulas, j is 1, 2 or 3. The side chain R⁴⁶ may be thesame or different and may also bond together to form a ring. R⁴⁶ isrepresented by the above formula (8a), (8b) or (8c). The side chain R⁴⁷may be the same or different and stands for hydrogen or a straight,branched or cyclic alkyl group of 1 to 20 carbon atoms which may containan ether or hydroxyl group. R⁴⁸, R⁵⁰ and R⁵³ are independently straightor branched alkylene groups of 1 to 4 carbon atoms. R⁴⁹ and R⁵² areindependently hydrogen or straight, branched or cyclic alkyl groups of 1to 20 carbon atoms which may contain one or more hydroxyl, ether, estergroups or lactone rings. R⁵¹ is a single bond or a straight or branchedalkylene group of 1 to 4 carbon atoms. R⁵⁴ is a straight, branched orcyclic alkyl group of 1 to 20 carbon atoms which may contain one or morehydroxyl, ether, ester groups or lactone rings.

[0086] Illustrative, non-limiting examples of the compounds of formula(8) include tris(2-methoxymethoxyethyl)amine,tris{2-(2-methoxyethoxy)ethyl)amine,tris(2-(2-methoxyethoxymethoxy)ethyl}amine,tris{2-(1-methoxyethoxy)ethyl}-amine,tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine,tris[2-{2-(2-hydroxyethoxy)ethoxy}-ethyl]amine,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosane,4,7,13,18-tetraoxa-1,10-diazabicyclo-[8.5.5]eicosane,1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane,1-aza-12-crown-4,1-aza-15-crown-5,1-aza-18-crown-6,tris(2-formyloxyethyl)amine, tris(2-acetoxyethyl)amine,tris(2-propionyloxyethyl)amine, tris(2-butyryloxyethyl)amine,tris(2-isobutyryloxyethyl)amine, tris(2-valeryloxyethyl)amine,tris(2-pivaloyloxyethyl)amine,N,N-bis(2-acetoxyethyl)-2-(acetoxyacetoxy)ethylamine,tris(2-methoxycarbonyloxyethyl)amine,tris(2-tert-butoxycarbonyloxyethyl)amine,tris[2-(2-oxopropoxy)ethyl]amine,tris[2-(methoxycarbonylmethyl)oxyethyl]amine,tris[2-(tert-butoxycarbonylmethyloxy)ethyl]amine,tris[2-(cyclohexyloxycarbonylmethyloxy)ethyl]amine,tris(2-methoxycarbonylethyl)amine, tris(2-ethoxycarbonylethyl)amine,N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]ethylamine,N,N-bis(2-acetoxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine,N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine,N,N-bis(2-hydroxyethyl)-2-(4-hydroxybutoxycarbonyl)ethylamine,N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxycarbonyl)ethylamine,N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl)ethylamine,N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl)ethylamine,N-(2-hydroxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-butyl-bis[2-(methoxycarbonyl)ethyl]amine,N-butyl-bis[2-(2-methoxyethoxycarbonyl)ethyl]amine,N-methyl-bis(2-acetoxyethyl)amine, N-ethyl-bis(2-acetoxyethyl)amine,N-methyl-bis(2-pivaloyloxyethyl)amine,N-ethyl-bis[2-(methoxycarbonyloxy)ethyl]amine,N-ethyl-bis[2-(tert-butoxycarbonyloxy)ethyl]-amine,tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonylmethyl)amine,N-butyl-bis(methoxycarbonylmethyl)amine,N-hexyl-bis(methoxycarbonylmethyl)amine, andβ-(diethylamino)-δ-valerolactone.

[0087] Also useful are one or more of cyclic structure-bearing basiccompounds having the following general formula (9).

[0088] Herein R⁴⁶ is as defined above, and R⁵⁵ is a straight or branchedalkylene group of 2 to 20 carbon atoms which may contain one or morecarbonyl, ether, ester or sulfide groups.

[0089] Illustrative examples of the cyclic structure-bearing basiccompounds having formula (9) include1-[2-(methoxymethoxy)ethyl]pyrrolidine,1-[2-(methoxymethoxy)ethyl]-piperidine,4-[2-(methoxymethoxy)ethyl]morpholine,1-[2-[(2-methoxyethoxy)methoxy]ethyl]pyrrolidine,1-[2-[(2-methoxyethoxy)methoxy]ethyl]piperidine,4-[2-[(2-methoxyethoxy)methoxy]ethyl]morpholine, 2-(1-pyrrolidinyl)ethylacetate, 2-piperidinoethyl acetate, 2-morpholinoethyl acetate,2-(1-pyrrolidinyl)ethyl formate, 2-piperidinoethyl propionate,2-morpholinoethyl acetoxyacetate, 2-(1-pyrrolidinyl)ethylmethoxyacetate, 4-[2-(methoxycarbonyloxy)ethyl]morpholine,1-[2-(t-butoxycarbonyloxy)ethyl]piperidine,4-[2-(2-methoxyethoxycarbonyloxy)ethyl]morpholine, methyl3-(1-pyrrolidinyl)propionate, methyl 3-piperidinopropionate, methyl3-morpholinopropionate, methyl 3-(thiomorpholino)propionate, methyl2-methyl-3-(1-pyrrolidinyl)propionate, ethyl 3-morpholinopropionate,methoxycarbonylmethyl 3-piperidinopropionate, 2-hydroxyethyl3-(1-pyrrolidinyl)propionate, 2-acetoxyethyl 3-morpholinopropionate,2-oxotetrahydrofuran-3-yl 3-(1-pyrrolidinyl)propionate,tetrahydrofurfuryl 3-morpholinopropionate, glycidyl3-piperidinopropionate, 2-methoxyethyl 3-morpholinopropionate,2-(2-methoxyethoxy)ethyl 3-(1-pyrrolidinyl)propionate, butyl3-morpholinopropionate, cyclohexyl 3-piperidinopropionate,α-(1-pyrrolidinyl)methyl-γ-butyrolactone, β-piperidino-γ-butyrolactone,β-morpholino-δ-valerolactone, methyl 1-pyrrolidinylacetate, methylpiperidinoacetate, methyl morpholinoacetate, methylthiomorpholinoacetate, ethyl 1-pyrrolidinylacetate, and 2-methoxyethylmorpholinoacetate.

[0090] Also, one or more of cyano-bearing basic compounds having thefollowing general formulae (10) to (13) may be blended.

[0091] Herein, R⁴⁶, R⁵⁵ and j are as defined above, and R⁵⁶ and R⁵⁷ eachare independently a straight or branched alkylene group of 1 to 4 carbonatoms.

[0092] Illustrative examples of the cyano-bearing basic compoundsinclude 3-(diethylamino)propiononitrile,N,N-bis(2-hydroxyethyl)-3-aminopropiononitrile,N,N-bis(2-acetoxyethyl)-3-aminopropiononitrile,N,N-bis(2-formyloxyethyl)-3-aminopropiononitrile,N,N-bis(2-methoxyethyl)-3-aminopropiononitrile,N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile, methylN-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropionate, methylN-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropionate, methylN-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropionate,N-(2-cyanoethyl)-N-ethyl-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropiononitrile,N-(2-acetoxyethyl) —N-(2-cyanoethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(2-formyloxyethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(3-hydroxy-1-propyl)-3-aminopropiononitrile,N-(3-acetoxy-1-propyl)-N-(2-cyanoethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(3-formyloxy-1-propyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-tetrahydrofurfuryl-3-aminopropiononitrile,N,N-bis(2-cyanoethyl)-3-aminopropiononitrile, diethylaminoacetonitrile,N,N-bis(2-hydroxyethyl)aminoacetonitrile,N,N-bis(2-acetoxyethyl)aminoacetonitrile,N,N-bis(2-formyloxyethyl)aminoacetonitrile,N,N-bis(2-methoxyethyl)aminoacetonitrile,N,N-bis[2-(methoxymethoxy)ethyl]aminoacetonitrile, methylN-cyanomethyl-N-(2-methoxyethyl)-3-aminopropionate, methylN-cyanomethyl-N-(2-hydroxyethyl)-3-aminopropionate, methylN-(2-acetoxyethyl)-N-cyanomethyl-3-aminopropionate,N-cyanomethyl-N-(2-hydroxyethyl)aminoacetonitrile,N-(2-acetoxyethyl)-N-(cyanomethyl)aminoacetonitrile,N-cyanomethyl-N-(2-formyloxyethyl)aminoacetonitrile,N-cyanomethyl-N-(2-methoxyethyl)aminoacetonitrile,N-cyanomethyl-N-[2-(methoxymethoxy)ethyl)aminoacetonitrile,N-cyanomethyl-N-(3-hydroxy-1-propyl)aminoacetonitrile,N-(3-acetoxy-1-propyl)-N-(cyanomethyl)aminoacetonitrile,N-cyanomethyl-N-(3-formyloxy-1-propyl)aminoacetonitrile,N,N-bis(cyanomethyl)aminoacetonitrile, 1-pyrrolidinepropiononitrile,1-piperidinepropiononitrile, 4-morpholinepropiononitrile,1-pyrrolidineacetonitrile, 1-piperidineacetonitrile,4-morpholineacetonitrile, cyanomethyl 3-diethylaminopropionate,cyanomethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, cyanomethylN,N-bis(2-acetoxyethyl)-3-aminopropionate, cyanomethylN,N-bis(2-formyloxyethyl)-3-aminopropionate, cyanomethylN,N-bis(2-methoxyethyl)-3-aminopropionate, cyanomethylN,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, 2-cyanoethyl3-diethylaminopropionate, 2-cyanoethylN,N-bis(2-hydroxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis(2-acetoxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis(2-formyloxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis(2-methoxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, cyanomethyl1-pyrrolidinepropionate, cyanomethyl 1-piperidinepropionate, cyanomethyl4-morpholinepropionate, 2-cyanoethyl 1-pyrrolidinepropionate,2-cyanoethyl 1-piperidinepropionate, and 2-cyanoethyl4-morpholinepropionate.

[0093] These basic compounds may be used alone or in admixture of any.The basic compound is preferably formulated in an amount of 0.001 to 2parts, and especially 0.01 to 1 part by weight, per 100 parts by weightof the base resin. Less than 0.001 part of the basic compound may failto achieve the desired effects thereof, while the use of more than 2parts would result in too low a sensitivity.

[0094] Component (E)

[0095] The dissolution inhibitor (E) is a compound with a molecularweight of up to 3,000 which changes its solubility in an alkalinedeveloper under the action of an acid, and typically selected fromphenols, carboxylic acid derivatives, andhexafluoroisopropanol-containing compounds in which some or all ofhydroxyl groups are substituted with acid labile groups and which have amolecular weight of up to 2,500.

[0096] Examples of the phenol or carboxylic acid derivative having amolecular weight of up to 2,500 include4,4′-(1-methylethylidene)bisphenol,(1,1′-biphenyl-4,4′-diol)-2,2′-methylenebis(4-methylphenol),4,4-bis(4′-hydroxyphenyl)valeric acid, tris(4-hydroxyphenyl)methane,1,1,1-tris(4′-hydroxyphenyl)ethane, 1,1,2-tris(4′-hydroxyphenyl)ethane,phenolphthalein, thimolphthalein,3,3′-difluoro[(1,1′-biphenyl)-4,4′-diol],3,3′,5,5′-tetrafluoro[(1,1′-biphenyl)-4,4′-diol],4,4′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]-bisphenol,4,4′-methylenebis(2-fluorophenol), 2,2′-methylenebis(4-fluorophenol),4,4′-isopropylidenebis(2-fluorophenol),cyclohexylidenebis(2-fluorophenol),4,4′-[(4-fluorophenyl)methylene]bis(2-fluorophenol),4,4′-methylenebis(2,6-difluorophenol),4,4′-(4-fluorophenyl)methylenebis(2,6-difluorophenol),2,6-bis[(2-hydroxy-5-fluorophenyl)methyl]-4-fluorophenol,2,6-bis[(4-hydroxy-3-fluorophenyl)methyl]-4-fluorophenol, and2,4-bis[(3-hydroxy-4-hydroxyphenyl)methyl]-6-methylphenol. The acidlabile groups are the same as formulae (2) to (4) described above.

[0097] Examples of useful hexafluoroisopropanol unit-containingcompounds are given below, with the acid labile groups being the same asformulae (2) to (4) described above.

[0098] Illustrative, non-limiting, examples of the dissolutioninhibitors which are useful herein include3,3′,5,5′-tetrafluoro[(1,1′-biphenyl)-4,4′-di-t-butoxycarbonyl],4,4′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bisphenol-4,4′-di-t-butoxycarbonyl,bis(4-(2′-tetrahydropyranyloxy)phenyl)methane,bis(4-(2′-tetrahydrofuranyloxy)phenyl)methane,bis(4-tert-butoxyphenyl)methane,bis(4-tert-butoxycarbonyloxyphenyl)methane,bis(4-tertbutoxycarbonylmethyloxyphenyl)methane,bis(4-(1′-ethoxyethoxy)phenyl)methane,bis(4-(1′-ethoxypropyloxy)phenyl)methane,2,2-bis(4′-(2″-tetrahydropyranyloxy))propane,2,2-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)propane,2,2-bis(4′-tert-butoxyphenyl)propane,2,2-bis(4′-tert-butoxycarbonyloxyphenyl)propane,2,2-bis(4-tert-butoxycarbonylmethyloxyphenyl)propane,2,2-bis(4′-(1″-ethoxyethoxy)phenyl)propane,2,2-bis(4′-(1″-ethoxypropyloxy)phenyl)propane, tert-butyl4,4-bis(4′-(2″-tetrahydropyranyloxy)phenyl)valerate, tert-butyl4,4-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)valerate, tert-butyl4,4-bis(4′-tert-butoxyphenyl)valerate, tert-butyl4,4-bis(4-tert-butoxycarbonyloxyphenyl)valerate, tert-butyl4,4-bis(4′-tert-butoxycarbonylmethyloxyphenyl)valerate, tert-butyl4,4-bis(4′-(1″-ethoxyethoxy)phenyl)valerate, tert-butyl4,4-bis(4′-(1″-ethoxypropyloxy)phenyl)valerate,tris(4-(2′-tetrahydropyranyloxy)phenyl)methane,tris(4-(2′-tetrahydrofuranyloxy)phenyl)methane,tris(4-tert-butoxyphenyl)methane,tris(4-tert-butoxycarbonyloxyphenyl)methane,tris(4-tert-butoxycarbonyloxymethylphenyl)methane,tris(4-(1′-ethoxyethoxy)phenyl)methane,tris(4-(1′-ethoxypropyloxy)phenyl)methane,1,1,2-tris(4′-(2″-tetrahydropyranyloxy)phenyl)ethane,1,1,2-tris(4′-(2″-tetrahydrofuranyloxy)phenyl)ethane,1,1,2-tris(4′-tert-butoxyphenyl)ethane,1,1,2-tris(4′-tert-butoxycarbonyloxyphenyl)ethane,1,1,2-tris(4′-tert-butoxycarbonylmethyloxyphenyl)ethane,1,1,2-tris(4′-(1′-ethoxyethoxy)phenyl)ethane,1,1,2-tris(4′-(1′-ethoxypropyloxy)phenyl)ethane, t-butyl2-trifluoromethylbenzenecarboxylate, t-butyl2-trifluoromethylcyclohexanecarboxylate, t-butyldecahydronaphthalene-2,6-dicarboxylate, t-butyl cholate, t-butyldeoxycholate, t-butyl adamantanecarboxylate, t-butyl adamantaneacetate,and tetra-t-butyl 1,1′-bicyclohexyl-3,3′,4,41-tetracarboxylate.

[0099] In the resist composition according to the invention, anappropriate amount of the dissolution inhibitor (E) is up to about 20parts, and especially up to about 15 parts by weight per 100 parts byweight of the base resin in the composition. With more than 20 parts ofthe dissolution inhibitor, the resist composition becomes less heatresistant because of an increased content of monomer components.

[0100] In general, resist compositions for F₂ lithography have theproblem that the developer cannot effectively penetrate through theresist film because fluorine is incorporated in the base polymer. Forresist compositions adapted for KrF and ArF exposure, methods of addingcompounds containing water-soluble groups such as phenolic hydroxyl,carboxyl, sulfonamide and carbonamide groups were proposed to solve theproblem of developer wettability. Examples include carboxylic anhydridesdescribed in JP-A 2000-47385 and JP-A 2000-275840, phosphine compoundsdescribed in JP-A 2000-275838, thiocarbonyl group-containing compoundsdescribed in JP-A 2000-275841, carboxyl group-containing compoundsdescribed in JP-A 11-338150, and sulfonamide compounds described in JP-A11-327145. However, all the foregoing compounds exhibit strongabsorption at 157 nm and thus have the drawback of reducing thetransmittance of resist compositions. It was thus proposed to use thehexafluoroisopropanol-containing compound described above in thedissolution inhibitor sector (whose hydroxyl group is not protected asopposed to the dissolution inhibitor) for the purpose of improving thedeveloper wettability. The hexafluoroisopropanol-containing compound ispreferably used in an amount of 5 to 40 parts, more preferably 8 to 30parts by weight per 100 parts by weight of the polymer. Outside therange, less amounts may fail to achieve the desired effect whereaslarger amounts may cause unexposed areas of the resist film to bedissolved after development and undergo phase separation from thepolymer so that the film as spin coated becomes mottled.

[0101] The resist composition of the invention may include optionalingredients, typically a surfactant which is commonly used for improvingthe coating characteristics. Optional ingredients may be added inconventional amounts so long as this does not compromise the objects ofthe invention.

[0102] A nonionic surfactant is preferred, examples of which includeperfluoroalkyl polyoxyethylene ethanols, fluorinated alkyl esters,perfluoroalkylamine oxides, perfluoroalkyl EO-addition products, andfluorinated organosiloxane compounds. Illustrative examples includeFlorade FC-430 and FC-431 from Sumitomo 3M Ltd., Surflon S-141 and S-145from Asahi Glass Co., Ltd., Unidyne DS-401, DS-403, and DS-451 fromDaikin Industries Ltd., Megaface F-8151 from Dainippon Ink & Chemicals,Inc., and X-70-092 and X-70-093 from Shin-Etsu Chemical Co., Ltd.Preferred surfactants include Florade FC-430 from Sumitomo 3M Ltd. andX-70-093 from Shin-Etsu Chemical Co., Ltd.

[0103] Pattern formation using the resist composition of the inventionmay be carried out by a known lithographic technique. For example, theresist composition may be applied onto a substrate such as a siliconwafer by spin coating or the like to form a resist film having athickness of 0.1 to 1.0 μm, which is then pre-baked on a hot plate at 60to 200° C. for 10 seconds to 10 minutes, and preferably at 80 to 150° C.for ½ to 5 minutes. A patterning mask having the desired pattern maythen be placed over the resist film, and the film exposed through themask to an electron beam or to high-energy radiation such as deep-UVrays, excimer laser beams, or x-rays in a dose of about 1 to 200 mJ/cm²,and preferably about 10 to 100 mJ/cm², then post-exposure baked (PEB) ona hot plate at 60 to 150° C. for 10 seconds to 5 minutes, and preferablyat 80 to 130° C. for ½ to 3 minutes. Finally, development may be carriedout using as the developer an aqueous alkali solution, such as 0.1 to5%, and preferably 2 to 3%, tetramethylammonium hydroxide (TMAH), thisbeing done by a conventional method such as dipping, puddling, orspraying for a period of 10 seconds to 3 minutes, and preferably 30seconds to 2 minutes. These steps result in the formation of the desiredpattern on the substrate. Of the various types of high-energy radiationthat may be used, the resist composition of the invention is best suitedto micro-pattern formation with, in particular, deep-UV rays having awavelength of 254 to 120 nm, an excimer laser, especially ArF excimerlaser (193 nm), F₂ excimer laser (157 nm), Kr₂ excimer laser (146 nm),KrAr excimer laser (134 nm) or Ar₂ excimer laser (126 nm), x-rays, or anelectron beam. The desired pattern may not be obtainable outside theupper and lower limits of the above range.

[0104] The resist composition according to the invention is sensitive tohigh-energy radiation, and has excellent sensitivity at a wavelength ofup to 200 nm, especially up to 170 nm. Owing to the use of a copolymerof an acrylate monomer containing fluorine at a-position with anorbornene derivative containing oxygen or sulfur within the norbornenering as the base resin, the resist composition is more transparent andmore adherent and at the same time, more resistant to plasma etching.These features of the inventive resist composition enable its useparticularly as a resist having a low absorption at the exposurewavelength of a F₂ excimer laser, and permit a finely defined patternhaving sidewalls perpendicular to the substrate to be easily be formed,making the resist ideal as a micropatterning material in VLSIfabrication.

EXAMPLE

[0105] Examples of the invention are given below by way of illustrationand not by way of limitation. The abbreviations used herein are AIBN for2,2′-azobisisobutyronitrile, GPC for gel permeation chromatography, NMRfor nuclear magnetic resonance, Mw for weight average molecular weight,and Mn for number average molecular weight.

Synthesis Example 1

[0106] Copolymerization of tert-butyl α-trifluoromethylacrylate andMonomer 1 (6:4)

[0107] In a 300-ml flask, 10.3 g of tert-butyl α-trifluoromethylacrylateand 9.7 g of Monomer 1, shown below, were dissolved in 13.3 g oftoluene. The system was fully purged of oxygen, charged with 0.29 g ofthe initiator AIBN, and heated at 60° C. at which polymerizationreaction took place for 24 hours.

[0108] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 16.2 g of a white polymer, whichwas found to have a Mw of 7,800 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.4 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist oftert-butyl a-trifluoromethylacrylate and Monomer 1 in a ratio of 61:39.

Synthesis Example 2

[0109] Copolymerization of tert-butyl α-trifluoromethylacrylate andMonomer 2 (6:4)

[0110] In a 300-ml flask, 9.6 g of tert-butyl a-trifluoromethylacrylateand 10.4 g of Monomer 2, shown below, were dissolved in 13.3 g oftoluene. The system was fully purged of oxygen, charged with 0.27 g ofthe initiator AIBN, and heated at 60° C. at which polymerizationreaction took place for 24 hours.

[0111] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 16.7 g of a white polymer, whichwas found to have a Mw of 7,500 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.4 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist oftert-butyl α-trifluoromethylacrylate and Monomer 2 in a ratio of 60:40.

Synthesis Example 3

[0112] Copolymerization of tert-butyl α-trifluoromethylacrylate, Monomer3 and Monomer 1 (4.5:1.5:4)

[0113] In a 300-ml flask, 7.3 g of tert-butyl α-trifluoromethylacrylate,3.5 g of Monomer 3, shown below, and 9.2 g of Monomer 1 were dissolvedin 13.3 g of toluene. The system was fully purged of oxygen, chargedwith 0.27 g of the initiator AIBN, and heated at 60° C. at whichpolymerization reaction took place for 24 hours.

[0114] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 15.4 g of a white polymer, whichwas found to have a Mw of 6,900 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.5 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist oftert-butyl α-trifluoromethylacrylate, Monomer 3 and Monomer 1 in a ratioof 46:14:40.

Synthesis Example 4

[0115] Copolymerization of tert-butyl α-trifluoromethylacrylate andMonomer 4 (6:4)

[0116] In a 300-ml flask, 13.1 g of tert-butyl a-trifluoromethylacrylateand 6.9 g of Monomer 4, shown below, were dissolved in 13.3 g oftoluene. The system was fully purged of oxygen, charged with 0.37 g ofthe initiator AIBN, and heated at 60° C. at which polymerizationreaction took place for 24 hours.

[0117] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 14.4 g of a white polymer, whichwas found to have a Mw of 7,300 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.4 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist oftert-butyl α-trifluoromethylacrylate and Monomer 4 in a ratio of 61:39.

Synthesis Example 5

[0118] Copolymerization of Monomer 5 and Monomer 1 (6:4)

[0119] In a 300-ml flask, 12.2 g of Monomer 5, shown below, and 7.8 g ofMonomer 1 were dissolved in 13.3 g of toluene. The system was fullypurged of oxygen, charged with 0.23 g of the initiator AIBN, and heatedat 60° C. at which polymerization reaction took place for 24 hours.

[0120] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 15.5 g of a white polymer, whichwas found to have a Mw of 7,200 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.5 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist ofMonomer 5 and Monomer 1 in a ratio of 60:40.

Synthesis Example 6

[0121] Copolymerization of Monomer 5 and Monomer 2 (6:4)

[0122] In a 300-ml flask, 11.5 g of Monomer 5 and 8.5 g of Monomer 2were dissolved in 13.3 g of toluene. The system was fully purged ofoxygen, charged with 0.22 g of the initiator AIBN, and heated at 60° C.at which polymerization reaction took place for 24 hours.

[0123] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 16.4 g of a white polymer, whichwas found to have a Mw of 7,700 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.4 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist ofMonomer 5 and Monomer 2 in a ratio of 58:42.

Synthesis Example 7

[0124] Copolymerization of Monomer 5, Monomer 3 and Monomer 1(4.5:1.5:4)

[0125] In a 300-ml flask, 10.2 g of Monomer 5, 2.0 g of Monomer 3 and7.8 g of Monomer 1 were dissolved in 13.3 g of toluene. The system wasfully purged of oxygen, charged with 0.23 g of the initiator AIBN, andheated at 60° C. at which polymerization reaction took place for 24hours.

[0126] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 16.2 g of a white polymer, whichwas found to have a Mw of 7,200 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.4 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist ofMonomer 5, Monomer 3 and Monomer 1 in a ratio of 43:15:42.

Synthesis Example 8

[0127] Copolymerization of Monomer 5 and Monomer 4 (6:4)

[0128] In a 300-ml flask, 14.7 g of Monomer 5 and 5.3 g of Monomer 4were dissolved in 13.3 g of toluene. The system was fully purged ofoxygen, charged with 0.28 g of the initiator AIBN, and heated at 60° C.at which polymerization reaction took place for 24 hours.

[0129] The polymer thus obtained was worked up by pouring the reactionmixture into hexane whereupon the polymer precipitated. The polymercollected was dissolved in tetrahydrofuran and poured into 2 liters ofhexane for precipitation. This cycle was repeated twice. The polymer wasseparated and dried. There was obtained 15.4 g of a white polymer, whichwas found to have a Mw of 7,200 as measured by the light scatteringmethod, and a dispersity (Mw/Mn) of 1.4 as determined from the GPCelution curve. On ¹H-NMR analysis, the polymer was found to consist ofMonomer 5 and Monomer 4 in a ratio of 60:40.

[0130] Evaluation

[0131] Polymer Transmittance Measurement

[0132] The polymers obtained in Synthesis Examples 1 to 8, designatedPolymers 1 to 8, respectively, were determined for transmittance. Threeother polymers were furnished for comparison purposes. ComparativePolymer 1 is a monodisperse polyhydroxystyrene having a molecular weightof 10,000 and a dispersity (Mw/Mn) of 1.1 in which 30% of hydroxylgroups are replaced by tetrahydropyranyl groups. Similarly, ComparativePolymer 2 is polymethyl methacrylate having a molecular weight of 15,000and a dispersity (Mw/Mn) of 1.7; and Comparative Polymer 3 is a novolacpolymer having a meta/para ratio of 40/60, a molecular weight of 9,000and a dispersity (Mw/Mn) of 2.5.

[0133] Each polymer, 1 g, was thoroughly dissolved in 20 g of propyleneglycol monomethyl ether acetate (PGMEA), and passed through a 0.2-μmfilter, obtaining a polymer solution. The polymer solution was spincoated onto a MgF₂ substrate and baked on a hot plate at 100° C. for 90seconds, forming a polymer film of 100 nm thick on the substrate. Usinga vacuum ultraviolet spectrometer (VUV-200S by Nihon Bunko K.K.), thepolymer layer was measured for transmittance at 248 nm, 193 nm and 157nm. The results are shown in Table 1. TABLE 1 Transmittance (%) 248 nm193 nm 157 nm Polymer 1 99 91 59 Polyer 2 99 90 57 Polymer 3 99 91 52Polymer 4 99 90 59 Polymer 5 99 91 58 Polymer 6 99 90 56 Polymer 7 99 9052 Polymer 8 99 91 59 Comparative Polymer 1 90 5 15 Comparative Polymer2 91 80 12 Comparative Polymer 3 82 6 17

[0134] It is evident from Table 1 that resist compositions usingpolymers within the scope of the invention have a high transparency atthe F₂ excimer laser wavelength of 157 nm.

[0135] Resist Preparation and Exposure

[0136] Resist solutions were prepared in a conventional manner byformulating the polymer, photoacid generator (PAG1 or PAG2), basiccompound, dissolution inhibitor (DRIL) and solvent in the amounts shownin Table 2.

[0137] TBA: tributylamine

[0138] TEA: triethanolamine

[0139] PGMEA: propylene glycol monomethyl ether acetate

[0140] On silicon wafers having a film of DUV-30 (Brewer Science) coatedto a thickness of 55 nm, the resist solutions were spin coated, thenbaked on a hot plate at 100° C. for 90 seconds to give resist filmshaving a thickness of 200 nm.

[0141] The resist films were exposed by means of an F₂ excimer laser(VUVES by Lithotec Japan Co., Ltd.) while varying the exposure dose.Immediately after exposure, the resist films were baked at 120° C. for90 seconds and then developed for 60 seconds with a 2.38% aqueoussolution of tetramethylammonium hydroxide. The film thickness wasmeasured in different dose areas. From the residual filmthickness-to-dose relationship, the sensitivity (Eth) was determined asthe exposure dose giving a film thickness 0. A γ value which was theslope (tanθ) of the characteristic curve was also determined. TABLE 2Photoacid Basic Dissolution Polymer generator compound inhibitor SolventEth, (pbw) (pbw) (pbw) (pbw) (pbw) mJ/cm² γ Polymer 1 PAG1 TBA — PGMEA22 10.5 (100) (2) (0.1) (1,000) Polymer 2 PAG1 TBA — PGMEA 18  8.5 (100)(2) (0.1) (1,000) Polymer 3 PAG1 TBA — PGMEA 23 12.3 (100) (2) (0.1)(1,000) Polymer 4 PAG1 TBA — PGMEA 28  8.9 (100) (2) (0.1) (1,000)Polymer 5 PAG1 TBA — PGMEA 18 13.5 (100) (2) (0.1) (1,000) Polymer 6PAG1 TBA — PGMEA 16 11.0 (100) (2) (0.1) (1,000) Polymer 7 PAG1 TBA —PGMEA 18 12.3 (100) (2) (0.1) (1,000) Polymer 8 PAG1 TBA — PGMEA 23 11.9(100) (2) (0.1) (1,000) Polymer 8 PAG1 TEA — PGMEA 22 13.5 (100) (2)(0.1) (1,000) Polymer 8 PAG1 TBA DRI1 PGMEA 19 12.0 (100) (2) (0.1) (10)(1,000) Polymer 8 PAG2 TBA — PGMEA 16 11.0 (100) (2) (0.1) (1,000)Comparative PAG1 TEA — PGMEA non- — Polymer 1 (2) (0.1) (1,000)sensitive, (100) turned negative without film thickness decreasing to 0nm

[0142] As is evident from Table 2, upon exposure to VUV, the resistcompositions within the scope of the invention exerted the positiveworking effect that the film thickness decreased with an increasingexposure dose.

[0143] Japanese Patent Application No. 2001-393302 is incorporatedherein by reference.

[0144] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A polymer comprising recurring units of the following generalformulae (1a) and (1b) and having a weight average molecular weight of1,000 to 500,000,

wherein R¹ and R² each are hydrogen, a fluorine atom or a straight,branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbonatoms, R³ is a fluorine atom or a straight, branched or cyclicfluorinated alkyl group of 1 to 20 carbon atoms, R⁴ is an acid labilegroup, an adhesive group or a straight, branched or cyclic fluorinatedalkyl group of 1 to 20 carbon atoms, R⁵ is an oxygen or sulfur atom,R^(6a), R^(6b), R^(6c) and R^(6d) are each independently hydrogen, ahydroxyl group, —(CH₂)_(d)C(R⁷)₂(OR⁸), —(CH₂)_(d)CO₂R⁸, or a straight,branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbonatoms which may contain oxygen in the form of a hydroxyl group or etherbond in a substituent group, R⁷ is hydrogen, a fluorine atom or astraight, branched or cyclic fluorinated alkyl group of 1 to 20 carbonatoms, R⁸ is hydrogen, an acid labile group, an adhesive group, or astraight, branched or cyclic fluorinated alkyl group of 1 to 20 carbonatoms, letters a and b each are a number from more than 0 to less than1, and 0<a+b≦1, c is 0 or 1, and d is a number of 0 to
 6. 2. The polymerof claim 1 wherein R³ is trifluoromethyl.
 3. A resist compositioncomprising the polymer of claim
 1. 4. A chemically amplified positiveresist composition comprising (A) the polymer of claim 1, (B) an organicsolvent, and (C) a photoacid generator.
 5. The resist composition ofclaim 4, further comprising (D) a basic compound.
 6. The resistcomposition of claim 4, further comprising (E) a dissolution inhibitor.7. A process for forming a resist pattern comprising the steps of:applying the resist composition of claim 3 onto a substrate to form acoating, heat treating the coating and then exposing it to high-energyradiation in a wavelength band of 100 to 180 nm or 1 to 30 nm through aphoto mask, and optionally heat treating the exposed coating anddeveloping it with a developer.
 8. The pattern forming process of claim7 wherein the high-energy radiation is an F₂ laser beam, Ar₂ laser beamor soft x-ray.